Power converters for converting AC power, such as 3-phase AC power, into DC power are well known. Commonly, such AC-to-DC power converters operate by controlling rectification devices such as power thyristors/silicon-controlled rectifier (SCRs) so that the devices alternately allow current to flow and preclude current from flowing between a given AC input line and the DC output lines. Such converters allow for a significant amount of control over the power output insofar as the SCRs can be controlled to switch on to conduct current (e.g., “fired”) at a variety of time instants (e.g., at a variety of “firing angles”).
A problem faced by conventional power converters is that, under certain circumstances, rapid changes in the input voltage without corresponding adjustments performed by the power converters themselves can result in excessively high current being drawn from the line (and eventually provided to a load). Such excessive “inrush currents” in particular can arise subsequent to unexpected, significant drops or “dips” in the AC input power level (or a characteristic of the AC input power, such as the voltage level of the input power). Such dips in the AC input power, or even total loss of power, can occur for a variety of reasons such as inclement weather, load imbalances, line malfunctions, or other reasons. When such dips in the AC input power level occur but then the AC input power recovers, the recovery of voltage can result in a significant inrush current to the power converter (and also eventually to the load), which can be damaging to the power converter and lead to undesired shut-down of the connected load.
A need therefore exists for an improved AC-to-DC power converter. In particular, a need exists for an improved AC-to-DC power converter capable of providing power conversion (e.g., by adjustment of the firing angle of semiconductor switching devices in the converter) and also, during the power conversion process, capable of responding to drops in the AC input power level in a manner that reduces or mitigates any inrush currents that can occur when the AC input power recovers.